Magnetic elements such as inductors and transformers are widely used in many electronic apparatuses such as power supply apparatuses or power adapters. Since the power supply apparatuses or power adapters are developed toward minimization and high power, the volumes of the magnetic devices for use in these electronic apparatuses are gradually reduced and the shapes thereof become flatter. Moreover, the magnetic element can be directly arranged on a circuit board according to a surface mount technology (SMT), and thus such a magnetic element is also referred as a surface mount magnetic device. For increasing throughput and yield, the surface mount magnetic device is mounted on the circuit board by an automatic placement process according to the surface mount technology (SMT).
A conventional automatic placement process will be illustrated as follows. First of all, multiple surface mount magnetic devices are successively transported to a specified zone by a feeding machine. Then, the surface mount magnetic devices are picked by an automatic placement machine and then placed on predetermined locations of the circuit board that have been previously coated with solder paste. Then, the circuit board and the surface mount magnetic devices are heated in a reflow furnace to melt the solder paste. Afterwards, the circuit board is cooled to solidify the solder paste so as to securely attach the surface mount magnetic devices onto the circuit board. As known, the step of placing the surface mount magnetic devices on the circuit board is very important. If the sequence of placing the surface mount magnetic devices is improper or the surface mount magnetic devices are not precisely placed on the contact pads, the assembling time is increased and the yield is reduced.
FIG. 1 is a schematic view illustrating a placement machine for placing a surface mount magnetic device on a circuit board according to the prior art. The placement machine 1 has a plurality of placement heads 11. These placement heads 11 have individual tubes 110, which are communicated with a driving device such as a vacuum pump (not shown). In addition, nozzles 111 are disposed at the tips of respective tubes 110. For picking up surface mount magnetic devices 2, the placement heads 11 are horizontally and vertically moved to locations above corresponding surface mount magnetic devices 2 such that the nozzles 111 are aligned with corresponding surface mount magnetic devices 2. For clarification and brevity, only a surface mount magnetic device 2 is shown in the drawings. Due to pneumatic suction of the vacuum pump, the nozzles 111 can vacuum suck the top surface 21 of the surface mount magnetic device 2 such that the surface mount magnetic device 2 is picked by the placement head 11. Next, the placement head 11 is moved until the nozzle 111 is aligned with a contact pad of a circuit board (not shown). Next, the vacuum pump inhales air to the tube 110 such that the surface mount magnetic device 2 is detached from the nozzle 111. Meanwhile, the surface mount magnetic device 2 is placed on the contact pad of the circuit board.
FIG. 2A is a schematic top view of the surface mount magnetic device as shown in FIG. 1. FIG. 2B is a schematic cross-sectional view of the surface mount magnetic device as shown in FIG. 1. As shown in FIG. 2A and FIG. 2B, the surface mount magnetic device 2 is substantially a magnetic element including two magnetic cores 22 and a winding structure 23. The winding structure 23 is enclosed by the magnetic cores 22. The winding structure 23 is produced by winding coils (not shown) on a bobbin 232 and then sheltering an insulating layer 231 around the coils. In addition, a fixing frame 25 is sheathed around the outer surface of the magnetic cores 22 so as to fix the magnetic cores 22. In a case that too many turns of coils are wound on the bobbin 232, the winding structure 23 is located at a higher level than the magnetic cores 22 with respect to the circuit board (not shown). Furthermore, if the fill adhesive or the assembly adhesive (not shown) is protruded from the top surface 21 of the magnetic element 2 or the coils are not equally wound around the bobbin 232, the top surface 21 of the magnetic element 2 is usually an uneven surface. Under this circumstance, the nozzle 110 of the placement head 11 fails to vacuum suck up the top surface 21 of the magnetic element 2 because it is difficult to create a vacuum seal condition between the top surface 21 and the nozzle 110. The insufficient pneumatic suction of the vacuum pump usually results in a component disposal. At this time, the production line is stopped and the pick and place task needs to be done again.
Please refer to FIG. 2A again. The surface mount magnetic device 2 further includes multiple pins 24. A first end of the pin 24 is connected with the winding structure 23. A second end of the pin 24 is disposed on a predetermined contact pad of the circuit board that has been previously coated with solder paste. Then, the circuit board and the surface mount magnetic device 2 are heated in a reflow furnace to melt the solder paste. Afterwards, the circuit board is cooled to solidify the solder paste so as to securely attach the surface mount magnetic device 2 onto the circuit board. After the surface mount magnetic device 2 is mounted onto the circuit board, the surface mount magnetic device 2 is also electrically connected with the circuit board. Since the volume of the surface mount magnetic device 2 is very small, the pin positions of the pins 24 and the polarity of the surface mount magnetic device 2 are difficult to be recognized. If the direction or the polarity of the surface mount magnetic device 2 is erroneous, the placement method fails to be normally operated.
Moreover, since the area of the top of the surface mount magnetic device is very small, it is difficult to label a model number on the surface mount magnetic device and the manufacturer fails to recognize the surface mount magnetic device. Under this circumstance, a material confusion problem occurs. In addition, since the area of the top of the surface mount magnetic device is very small, the nozzle of the placement machine fails to effectively suck up the surface mount magnetic device and transport the surface mount magnetic device to the predetermined position of the circuit board. In most situations, the surface mount magnetic device needs to be manually placed on the circuit board by tweezers. In other words, the conventional surface mount magnetic device is labor-intensive and time-consuming.
There is a need of providing a surface mount magnetic device and a placement method of the surface mount magnetic device so as to obviate the drawbacks encountered from the prior art.